A method includes detecting high-voltage faults, such as welded contactors or disconnected components, in a vehicle by measuring the total electrical impedance between positive and negative rails of a high-voltage bus and a ground or chassis, comparing the impedance before and after opening the contactors, and executing a maintenance response. The response includes setting an error code when the open impedance level is less than a threshold multiple of the closed impedance level. A vehicle includes a chassis, energy storage system (ESS), motor/generator, and a high-voltage bus conducting electrical current from the ESS to the motor/generator. Contactors are positioned along each of the rails of the bus, a device for measuring a total electrical impedance level between the chassis and each of the rails, and a controller for determining a welded contactor condition of at least one of the contactors based on the measured total electrical impedance level.